Valve mechanism



July 28, 1964 v, BuNTlNG 3,142,316

VALVE MECHANISM Original Filed Aug. 20, 1954 I5 Sheets-Sheet 1 INVENTOR.ERNEST V. BUNTING ATTOlP/VfKi y 23, 1954 E. v. BUNTING 3,142,316

VALVE MECHANISM Original Filed Aug. 20, 1954 3 Sheets-Sheet 2 INVENTOR.ERNEST v. BUNTING BY F /V%MM,/4uwm July 28, 1964 E. v. BUNTING 3,142,316

VALVE MECHANISM Original Filed Aug. 20, 1954 3 Sheets-Sheet (5 7o 7 4970 85 kw 60 fl 1 9/ 74 29 66 72 52 65 80 INVENTOR.

69 59 6"8 V 5658a ERNEST v. BUNTING BY 7 4 W w/ 144 9 0W United StatesPatent 3,142,316 VALVE MECHANISM Ernest V. Bunting, Detroit, Mich,assignor to Massey- Ferguson inc, Detroit, Mich, a corporation ofMaryland Original application Aug. 20, 1954, Ser. No. 451,276, nowPatent No. 2,996,124, dated Aug. 15, 1961. Divided and this applicationNov. 9, 1960, Ser. No. 68,184

4 Claims. (Cl. l37--625.l8)

The invention relates to control valve mechanism for hydraulic systemsof the type provided in tractors for raising and lowering attachedimplements and for regulating their working depths. The presentapplication is a division of my copending application, Serial No.451,276, filed August 20, 1954, now Patent No. 2,996,124 of August 15,1961.

One object of the invention is to provide valve mechanism for hydraulicsystems of the above general character which affords a wider range, aswell as more precise control of the implement raising and lowering powerunit.

Another object is to provide a valve construction which minimizessticking or other malfunctioning of the movable valve member and whichmaterially simplifies the manufacture and assembly of the valves.

It is also an object of the invention to provide valve mechanism that iscapable of giving long and efficient service under the severe operatingconditions inherent in its use in tractor hydraulic systems.

Other objects and advantages of the invention will be come apparent fromthe following detailed description of the preferred embodimentillustrated in the accompanying drawings, in which FIGURE 1 is ahorizontal sectional view through the center housing of a tractorequipped with a hydraulic hitch-actuating power unit and control valvemechanism embodying the features of the invention.

FIG. 2 is a longitudinal sectional view of the control valve mechanism.

FIG. 3 is a fragmentary sectional view taken in a plane substantially onthe line 3-3 of FIG. 2.

FIG. 4 is a stop motion view of the valve mechanism in the overloadrelease position.

While a single preferred embodiment of the invention has been shown andwill be described herein in detail, it is not intended to limit theinvention to the particular structure shown, the intention being tocover all modifications and alternative constructions falling within thespirit and scope of the invention as more broadly and generallycharacterized in the appended claims.

By way of illustration the invention has been shown as incorporated inthe hydraulic operating and control system of a Ferguson tractor. Asshown in FIG. 1, the tractor has a center housing 10, which, with theengine and central gear box, constitute the backbone of a framelesstractor body. Such tractors are conventionally equipped withpneumatically tired Wheels, the rear or driving wheels of which aredriven from the tractor engine through change speed gearing (not shown)by way of a power delivery shaft 12, a differential 13 and axle shafts14.

The exemplary tractor is equipped with an implement hitch linkage of thetype commonly provided on Ferguson tractors. This linkage includes apair of trailing lower or draft links 15 and an upper or top link 16.The draft links 15 are pivoted at their forward ends as at on the rearportion of the tractor center housing to swing both vertically andhorizontally. At their trailing ends the draft links are provided withsuitable connecting elements for disengageable connection with groundworking or other types of implements that are to be coupled to theractor.

ice

In use, the top link 16 of the hitch linkage has its trailing endconnected with the implement at a point substantially above the draftlink connections so that the forward tilting of the implement due tosoil reaction on its ground engaging parts is transmitted to a springbiased control plunger 22 on the tractor. As herein shown the plunger 22is supported for axial movement in an extension 26a of the centerhousing cover plate 26 with one end projecting at the rear of thehousing. The projecting plunger end is connected by a coupling pin 21with the top link 16 and with a rocker 25 which, in turn, is pivoted asat 24 on the cover plate extension.

Biasing of the plunger is effected by a heavy coil spring 29 interposedbetween spaced abutments on the plunger presented in this instance by ahead 27a threaded on the plunger and a cup-shaped member 28 with whichthe plunger has a lost motion connection. The extension 26a alsopresents stationary abutments or stops for cooperation with the spring,one of the abutments comprising a collar 30 threaded into the extensionand encircling the head 27a. The other stop comprises a closure plate31a bearing against a shoulder on the housing and providing a seat forthe member 28.

In the above arrangement the spring 29 is double acting. Thus, whentension is applied to the top link 16. plunger 22 and member 28 aredrawn rearwardly, compressing the spring between the member 28 and thecollar 34 Conversely, when compression is applied to the top link, theplunger 22 is shifted forwardly and the spring 29 is compressed betweenthe head 27a and the member 23 when the latter bottoms on the closureplate 31a. Such movements of the plunger 22 are transmitted through apush rod 131 to the control mechanism for effecting the raising orlowering of the hitch to adjust the draft load on the hitch linkage aswill appear presently.

Raising and lowering of the hitch linkage is efiected by a hydraulicpower unit. As shown in FIG. 1, the unit comprises a cylinder 36 securedto the underside of the center housing cover plate. The cylinder, whichopens to the rear, is fitted with a working piston having its piston rod38 projecting rearwardly therefrom. The ballshaped outer end of thepiston rod is socketed in the end of an arm 39 rigid with a transverserock shaft 40 journaled in the upper rear portion of the tractor body.The ends of this rock shaft project at opposite sides of the centerhousing and each has a crank arm 41 splined thereon. The crank arms areconnected to the respective draft links 15 by drop links 42.

The relationship between the power unit and the hitch linkage is suchthat when pressure fluid (such as oil) is supplied to the closed end ofthe cylinder 36, the piston is forced rearwardly to rock the armsupwardly and thus raise the lower draft links 15 and the implementcoupled thereto. Similarly, upon exhaust of fluid from the cylinder 36the piston is permitted to retreat into the cylinder under the urging ofthe gravity load on the links 15 so that the links swing downwardly in alowering direction.

The volumetric rate at which oil is supplied to or exhausted from theram cylinder 36 will accordingly determine the rate at which the draftlinks 15 are raised or lowered. In the exemplary tractor, pressure fluidis supplied to the power unit from a positive displacement pump 4-5under control of a novel valve mechanism V. As shown in FIG. 1, the pump45 is located in the center housing below the cylinder 36. The lowerportion of the housing is flooded with oil constituting a sump for thesystem. Oil enters the pump through an intake passage 47 (FIG. 2)controlled by the valve V and is discharged from the pump through aconduit 48 leading to the closed end of the cylinder 36. Oil isexhausted from the cylinder 36 through the conduit 48 and an exhaustpassage 49, also controlled by the valve V. A

spring loaded safety valve 45a relieves the high pressure side of thepump when excessive pressure is reached.

As will be seen by reference to FIG. 2 of the drawings, the valve V islocated in the lower portion of the pump housing. Its function is tometer fluid into or out of the system or to block it altogether. Inaccordance with the invention, novel features of construction have beenincorporated in the valve mechanism to effectively avoid any binding orsticking of the parts so that high fidelity operation will be insuredeven under the most trying field conditions.

In its preferred form the valve V comprises an axially slidable plunger55. It is generally tubular in shape with an interior centralenlargement or partition 56 through which extends an axial opening ofsquare cross section. The plunger may be machined from bar stock andsuitably hardened, being made to very accurate dimensions. In theassembled valve the plunger is slidably received in a pair of hardenedaccurately fitted steel rings 63 and 65 which define opposite ends of ahigh pressure chamber 62. A third ring 64 coacts with the central ring63 to define the opposite ends of a second or low pressure intakechamber 61. This third ring 64 is, however, free to float transaxiallywithin the confines of an outer ring 68. The nose of the plunger 55adjacent the floating ring 64 is tapered so that it can enter the ringfreely as it passes in and out of the chamber 61, centering the ring asit does so. Accordingly, accurate concentricity of mounting is requiredfor only a pair of rings (63, 65) rather than for a set of three, whichwould be a far more difficult task.

By using rings as shown to constitute the lands at opposite ends ofchambers through which the plunger 55 passes, liability to sticking andmalfunction of the plunger are minimized. The contact areas of the ringswith the plunger being of short axial length, they can be formed withgreater accuracy (to tolerances of a few thousandths of an inch) andless liable to ovaling or other faults than would be the case with abushing bored to receive the plunger.

Spacing sleeves 66 and 67 are interposed between the rings 64, 63 and63, 65, respectively. Being completely out of contact with the plunger55 their interior bores need not be of any great accuracy either as tosize or straightness. The sleeve 66 has large ports 71 for free passageof oil from the chamber 61 into the annular space surrounding the sleeveand thence into the pump intake passage 47. Likewise, the other sleeve67 has large ports 72 for unrestricted flow of oil into high pressurechamber 62 from the discharge passage 49. The latter is cored in thepump housing and communicates with the conduit 48.

The rings 63, 64 and 65 with their interposed spacer sleeves 66 and 67,are assembled in stacked relation as shown in FIG. 2 within a suitablebore 57 in a boss 58 integral with the pump housing and are held inplace therein by a cover plate 69 bolted to the housing. Sealing at theends of the high pressure chamber 62 is insured by elastic O-rings 70interposed between the flanged ends of the sleeve 67 and the adjacentfaces of the steel rings 63, 65. The whole assembly is pressed by thecover plate 69 against a shoulder 60 at the inner end of the housingbore.

In its central or neutral position, imperforate surface portions of theplunger 55 bridge between the rings 63, 65 and 63, 64. Consequently,entry of oil into the intake chamber 61 and exit of oil from the highpressure chamber 62 are both prevented. Under such conditions, fluid islocked in the system and the ram piston remains stationary to hold thehitch linkage in a fixed position.

As the valve plunger 55 is moved axially rearward or to the left asshown in FIG. 2 from such neutral position, there is a progressiveuncovering of a pair of narrow, axially extending slots 74. As theseslots pass under the ring 65, greater and greater slot area is opened tothe high pressure chamber 62. Accordingly, as soon as these slots ordrop ports begin to open in that fashion, high pressure oil spurtsthrough them from the pressure chamber 62, passes into the interior ofthe plunger, and then through a passage 58a back into the sump. Suchbleeding of fluid from the system permits the ram cylinder to retractinto the cylinder 36, lowering the hitch links 15.

The rate of such lowering depends upon the rate at which oil can escapeto the sump. By using slots 74 of long thin shape as shown for such dropor escape ports, the rate can be controlled with great nicety in slidingthe plunger back and forth to vary the area of the slots exposed. Asecond pair of slots 75 shorter and wider than the slots 74 are alsoprovided in the drop end of the plunger 55. When the plunger has movedfar enough rearward so that these slots 75 also begin to be exposed, therate of oil escape abruptly increases. A fast dumping of the systemensues.

Abutment against the central ring 63 by the shouldered left end of astop collar 76 (seated in a groove girdling the central portion of theplunger) limits the rearward travel of the plunger. That limit positionis one in which the plunger is still guidingly received in theaccurately fitted ring 65. The stop collar 76 likewise abuts against thering 65 to limit travel of the plunger in the opposite or forwarddirection. In that limit position (see FIG. 4), however, the plunger hasleft the ring 64 but can readily reenter it because that ring is freelyfloating.

As the plunger 55 moves forward from its neutral position, high pressurechamber 62 remains closed. But a pair of large slots 73 in the end ofthe plunger pass under the ring 64, establishing intake for the pump. Asthese slots 73 are so uncovered, oil passes (from the surrounding bodyof oil in the sump in which the mechanism is immersed) through the slotsinto the chamber 61 through the large ports 71 and thence into theintake passage 47. Oil so taken in is delivered by the pump to the ramcylinder 36 raising the hitch links 15. The functioning of the valve foroverload release purposes in which the plunger 55 travels to its extremeforward position will be described later.

As herein shown the plunger 55 is yieldably urged towards its rearwardor drop position by a compression spring 77 acting between a fixedabutment and a head 78 on the inner end of a push rod 79 operativelyconnected with the plunger. The operative connection in this instance isprovided by a head 80 of truncated shape, mating with a passage ofsquare cross section in the central partition 56 of the plunger.

For shifting the plunger against the bias of the spring 77 there isprovided a push rod 81 having a semispherical head 82 engaging in aconical socket 33 at the other end of the partition 56 of the plunger.At its outer end the push rod 81 is pivotally connected by a pin 84 tothe lower end of a valve lever 85 by which an operating connection ismade to the control mechanism later described. The lever 85 is pivotedintermediate its ends as at 86 on a supporting member 87 herein shown asa rod projecting from the pump housing. A nut 88 threaded on the rodaffords adjustment of the pivot fore-and-aft relative to the axis of thevalve.

Provision is made for continuously oscillating the valve plunger 55about its longitudinal axis to insure smooth and easy sliding of theplunger at all times. For this purpose the biasing spring 77 is housedin a cylinder 8? within which is received the square head 78 on the pushrod 79. Four grooves in the cylinder receive the corners of the head sothat it can slide freely lengthwise of the cylinder but is neverthelessconstrained to rock or oscillate about the cylinder axis. Restrictedclearance is also thus afforded between the edges of the head '78 andthe cylinder through which oil can How to give a dashpot effect for theplunger and thus damp movement of the valve plunger. The head 80 of thepush rod provides a rotary driving connection whereby the valve plunger55 is oscillated with the push rod upon oscillation of the cylinder. Asnap ring 90 within the cylinder defines a fixed abutment for the spring77. A second snap ring 96a at the opposite end of the cylinder catchesthe corners of the square head '73, holding it from emerging from thecylinder during assembly of the parts.

As shown in FIGS. 2 and 4, the cylinder 89 1s rotatably supported at oneend in a recess 91 in the valve casing concentric with the valve bore57. At its other end the cylinder is likewise rotatably supported in arecess 92 in a boss 93 which may constitute a part of the pump housingor a part of a bracket rigidly attached to the housing. A snap ring $4in the recess 92 takes the reaction of the cylinder 89. Interposedbetween the snap ring and the end of the cylinder is a disc 94a. Thelatter closes the cylinder end so that it may function as a dashpot asmentioned above. I

The cylinder and parts connected thereto are oscillated in timedrelation to the rotation of the pump shaft by means of an arm 95 havingan enlarged end portion apertured to receive the cylinder 89 andnonrotatably secured thereto by suitable means such as a locking screw96. At its other end the arm 95 is pivotally connected with a connectingrod 97 which has a ring portion encircling one of the eccentrics 98 onthe pump shaft 99. As the pump shaft rotates the eccentric acts throughthe connecting rod to oscillate the rod 95 and cylinder 89 and suchoscillations are transmitted by the push rod 79 to the valve plunger 55.

Two types or sources of control are present in the exemplary hydraulicsystem for operating the valve V, one manual and the other automatic. Sofar as automatic control is concerned, soil reaction on the implement ismeasured by the control spring 29 through the force applied through thetop link 16 of the hitch. As indicated above, changes in the forces onthe top link are reflected in the axial movements of the push rod 131which acts to shift the valve V, as will appear presently. Likewise,vertical positioning of the hitch linkage is automatically measured bythe rotational position of an edge cam 120 fast on the rock shaft 4%)and therefore always positioned in agreement with the draft links. Cam120 is also utilized in operating the control valve V.

So far as concerns manual adjustment or control, the driver uses a mainquadrant lever 181B fixed on the outer end of a shaft 101 journaled inthe housing cover plate. A slotted sheet metal quadrant 1% serves as aguide for the lever.

Alongside the main quadrant is a second or auxiliary quadrant 142slotted as at 144. Riding on this second quadrant is what may be calleda draft setter desig' nated generally as 141. This draft setter has twosheet metal handles or fingerpieces 141a and 141b. The first fingerpieceis integral with a slide 1410 of T-shape having a pair of spaced tangs141d guidingly received in the slot 144. A bolt having a squaredshoulder engaging in a complemental recess in the slide extends throughslot 144 for cooperation with a knurled knob or not 143 which releasablysecures the slide 1410 in selected positions of adjustment. The otherfingerpiece 141]; is fastened on the end of a lever non-rotatably fixedto the outer end of ashaft 149. A bolt 141 passing through the slot 144,a complemental slot 141g in the slide 1410 and an aperture in the leveris operative to frictionally clamp the lever in adjusted positions.

To use the draft setter the driver loosens the knob 143, grasps the pairof fingerpieces 141a and 141!) and then slides them downwardly to aposition corresponding to the working depth (actually the draft load)which he requires for the implement. Then he retightens the knob 143.Should he wish to make some short time field adjustment, he grasps thefingerpiece 1411) alone, pushing it up or down as required. Then torestore the original setting he has only to squeeze the fingerpiecestogether, bringing the fingerpiece 141b back into registry with 141a.

The draft setter 141 is in general left at the working depth found bestfor the particular implement being used. The driver pulls up or lowersthe main quadrant lever 1110 to raise or lower the implement. Once inthe soil the system will automatically retain the draft load fixed bythe draft setter 1 31. Occasions for changing the setting of the latterare, of course, comparatively infrequent.

In considering the mechanism here illustrated for funtionally connectingthe valve mechanism V with the various manual and automatic sources ofcontrol, it will be expedient first to trace the mechanical connectionsfrom the quadrant lever and position cam 120 by which the basicfollow-up or position control action between the quadrant lever and thehitch linkages is effectuated. As above stated, the quadrant lever ismounted on the quadrant lever shaft 101 which has an eccentric portionjournaling a roller positioned between a pair of jaws formed on the endof a cam lever which is pivotally connected to the upper end of anintermediate valve actuating lever 112. The downturned forward end 121of the lever 110 is hooked over an eccentric secured in selectedposition on the lever 112. Lever 112 is pivotally supported on anormally stationary pivot with its lower end positioned in the path of aroller 114 mounted on the upper end of a valve lever 85. Lever 112 hasits lower end guided in a slot 111 formed in a horizontally disposedflange 112' of a bracket 113. The action of the valve biasing spring 77in urging the valve plunger 55 in a direction to swing the lever 85clockwise (as viewed in FIG. 2) tends to rock the lever 112counterclockwise and thus imposes a bias on the lever 112.

The edge of the lower jaw of the cam lever 110 is formed to present asloping cam surface adapted to ride on a follower roller carried by arocker 117. The rocker is mounted to swing on a pivot shaft 118supported on and extending across the upper part of the housing coverplate. A second follower on the rocker 117 spaced rearwardly from thefirst mentioned roller coacts with the position control cam 120 on therock shaft 40. The cam is so shaped that it swings the rocker forwardlyas the hitch links are lowered and permits the rocker to swingrearwardly as the links are raised.

With the above arrangement of the control elements, movement of thecontrol lever of its uppermost position swings the cam lever 110 in acounterclockwise direction, assuming that the hitch links are in alowered position. The cam 120 will then be holding the rocker 117forwardly and the follower roller thereon will shift the cam lever 110forwardly. This rocks the lever 112 clockwise and the lever 85counterclockwise to shift the valve plunger 55 to raise position. Thepower operating system accordingly responds to raise the hitch.

As the hitch links rise, the cam 120 turns in unison so that the rocker117 and cam lever 110 move rearwardly under the urging of the valvespring 77. Accordingly, the valve plunger is progressively shiftedtowards and to its neutral position by the spring. In this instance thevalve arrives at neutral as the hitch reaches transport position.

To lower the hitch the lever 10%? is swung forwardly and downwardly ortoward the position shown in FIG. 1. This raises the rear end of the camlever 110 and allows the cam lever to move rearwardly. Such rearwardmovement of the cam lever and consequent rocking of the levers 112 and85 permits the valve plunger 55 to shift toward the drop position. Thecontrol valve opens to exhaust fluid from the ram, thus permitting thehitch linkage to descend.

As the hitch descends the cam 120 progressively shifts the cam lever andassociated elements including the valve plunger 55 toward the neutralposition so as to'interrupt the exhaust of fluid from the ram when thehitch reaches the position corresponding to the position to which thecontrol lever 100 has been moved. Full lowering is accomplished when thelever is advanced to the position shown in FIG. 1. It will thus be seenthat the hitch may be raised or lowered by swinging the control lever109 through the upper portion of its range. The hitch linkage followsprecisely the movements of the control lever and comes to rest in aposition corresponding to that in which the lever is stopped. Moreover,the movements of the hitch linkage approximates the movements of thelever as to rate so that the driver can raise or lower the hitch linkagerapidly or slowly if desired and can, of course, stop the movement inany desired position.

The position control action above described is that which would occurwith the draft setter 141 set so low or for such a heavy draft load thatit is not reached during the actual working contemplated. When, however,the draft setter is moved to a position representing a draft load whichwill be and is encountered as the implement penetrates the soil, theoperations are modified in the following manner. Push rod 131,previously mentioned, is pivotally connected to a rocker 130 pivotallysupported on the shaft 118. Inward movement of the push rod 131 underthe influence of the draft load on the hitch therefore swings the rockerforwardly. Rocker 130 carries a follower roller adapted to ride over awedge or sloping cam surface on a cam lever 135. This cam lever ispivotally connected at its forward end to a lever 136 which in turn ispivoted intermediate its ends on a normally stationary pivot closelyadjacent the pivot for the lever 112. The lever 136 is arrangedalongside the lever 112 with its lower end guided in the slot 111 in thebracket flange and extending through it for cooperation with the roller114 on the valve actuating lever 85. The spring bias on the lever 85(from the spring 77) urges the lever 136 counterclockwise and thusbiases the cam lever 135 rearwardly.

To provide for selectively determining the draft load to be maintainedon the hitch, the cam lever 135 has a rearwardly extending fingerportion defining a cam surface cooperating with a roller carried by aneccentric on the shaft 140 upon which the draft setter 141 is mounted.Rocking of the shaft 140 by the depth setter is thus effective to varythe position of the cam surface of the cam lever with reference to thecooperating roller. Accordingly, the position at which the lever 136intercepts the valve lever 85 may be varied by using the depth setter toswing the cam lever 135 on its pivot. This adjustment determines theinward displaced position of the control rod 131 required to return theplunger 55 to neutral position or, in other words, the draft load to bemaintained on the hitch linkage.

Differences in implements require variations in the responsecharacteristics of the system in order to realize satisfactory operationfor all. For example, if the system is sensitive enough to respondadequately for a light cultivator, it will overcontrol so badly for abig threebottom plow as to cause erratic and poor performance.Conversely, if the system is calculated for the heavy implement a lightone is substantially impotent to bring about any kind of control action.Heavy implements of light draft and vice versa extend the problem. Theproblem also becomes more acute as tractor power is increased, for withlarger tractors, an increasingly wide range of implement sizes can orrather should be accommodated.

Those problems have been solved in the present system by a basically newapproach. In substance, what is done is to interpose a positive stop foradjustably limiting the movement of the valve mechanism in the dropdirection. Stated more fully, what is done is to provide first of all acontrol valve mechanism which dumps oil at a variable rate dependingupon the extent of motion imparted to a movable member of the mechanism.

Referring more particularly to FIG. 2 of the drawings, the travel of theplunger 55 is adjustably limited in a leftward or drop direction. For aheavy three-bottom plow, for example, the limit is set so that, at most,only a portion of the narrow slot 74 can be uncovered when the draftcontrols call for a corrective lowering of the implement. Accordingly,even though the implement is very heavy and the oil thus expelled underhigh unit pressure, it will not overcontrol, will not dig too deepbefore the corrective lowering can be arrested. With a lighter implementthe limiter is set to permit greater travel of the plunger 55 so thatmore of the length of the slot 74 can be uncovered. Indeed, if desired,some of the slot 75 can also be uncovered. Consequently, even though thelighter implement does impose a lesser pressure on the oil in the system(and hence will not cause oil to be expelled during drop at the samerate as would a heavy implement), enlargement of the available drop portarea compensates.

The volumetric rate at which oil can be discharged for drop can thus bemade substantially the same for all implements regardless of the weightand suck which they may impose on the tractor. In the exemplarymechanism the auxiliary valve lever 112 is utilized to provide the limitstop for the valve lever under conditions in which it has been freedfrom its position control functions. Variable setting of the auxiliarylever is effected by movements of the main quadrant lever beyond thelimit position shown in FIG. 1. Thus, when the quadrant lever is pusheddown from the illustrated position, it will lift the cam lever tointerrupt its coupling with the position control cam 120. Such liftingof the cam lever also brings its hooklike element 121 into engagementwith an adjustable eccentric 122 (FIG. 1) on the lever 112 as the camlever swings beyond its lower position control limit. Cam lever 110 andthe lever 112 then rock as a unit about the pivot of the latter duringany further subsequent downward movement of the lever 100. Thus, furtherdownward movement of the lever 100 swings the lower end of the lever 112rearwardly as indicated by the several broken line positions in whichthe lever is shown in FIG. 2. The lever 112 then serves as a stop orabutment to progressively restrict the movement of the valve plunger 55toward exhaust position. Maximum restriction of the exhaust through thecontrol valve is accordingly obtained when the lever 100 is moved to itsextreme lowered position, thereby restricting movement of the valveplunger to a position in which only a small portion of the valve slot 74is exposed to the pressure chamber of the valve. Minimum restriction ofexhaust is available when the cam lever hook first contacts the lever112 (as in FIG. 1) for in that adjustment the valve plunger 55 can beactuated to its full exhaust position.

The improved valve mechanism is also operable to abruptly relievepressure in the system when a sudden overload is imposed on the tractoras by the implement hitting a rock or other fixed obstruction. By sorelieving the pressure, the implement which has been carried on thecolumn of oil in the cylinder 36 is dropped and consequently the weightcarried on the tractor drive wheels is dropped. The sudden drop incarried Weight permits the tractor drive wheels to spin and the momentumof the equipment is dissipated without further tugging and straining atthe obstruction.

When the obstruction is hit the sudden increase in draft generates aforce which is transmitted through the plunger 22 and control rod 131 tocontrol mechanism to shift the valve plunger 55 to the extreme rightwardposition in which it is shown in FIG. 4. It will be observed that insuch position the wide slots 73 which normally serve as intake slots aremoved beyond the central ring 63 into the high pressure chamber 62.Accordingly, in such position of the valve plunger pressure in thesystem is relieved through the slots 73 to the sump. Not only is thepump output diverted to the sump but the fluid in the cylinder 36 isquickly dumped to drop the hitch linkage and reduce the load on thetractor drive wheels.

It will be apparent from the foregoing that the invention provides valvemechanism of a novel and advantageous character for hydraulic systems ofthe type employed in tractors. The valve mechanism provides a wide rangeof control and is accurate and precise in its operation. Through thenovel construction and relation of the movable and fixed members of thevalve, sticking or other malfunctioning of the movable valve member iseffectively avoided. Moreover, manufacture and assembly of the valvemechanism is greatly simplified. The valve mechanism is simple andrugged in construction and capable of giving long and efficient serviceunder the severe operating conditions inherent in its use in a tractorhydraulic system.

I claim as my invention:

1. A valve comprising a housing having an elongated cylindrical boredivided into two axially aligned chambers, a tubular valve memberslidable axially through said bore, said member having slots at oppositeends spaced apart sufficiently to enable the non-slotted portions of themember to close the outer ends of both chambers by effecting a seal withthe outer ends of said cylindrical bore when the member is located in acentral position, stop means on said valve member coacting with stopmeans in the valve bore to define the limit positions of the member ateither side of said central position, said member in one of its limitpositions exposing the slots in one of its ends to one of said chambersto open the outer end of said chamber while maintaining the outer end ofthe other chamber closed, and said valve member in the other of saidlimit positions exposing the slots in its other end to both of saidchambers to open the outer end of said other chamber and to interconnectboth chambers at their inner ends.

2. A valve comprising a housing having an elongated cylindrical bore,three thin metal rings disposed in said bore and axially spaced apart todefine lands dividing the bore into two valve chambers, a tubular valveplunger slidable axially through said rings in engagement with saidlands, said valve plunger having slots at opposite ends spaced apartsufliciently to enable the non-slotted portions of the plunger to effecta seal with all three of said rings when in a central position, stopmeans on said valve plunger coacting with stop means in the valve boreto define the limit positions of the plunger at either side of saidcentral position, said valve plunger in one of said limit positionspositioning the slots in one of its ends so as to span one of the endrings to disrupt the seal therewith while maintaining the seal at theother two rings, and said valve plunger in the other of said limitpositions positioning the slots in its other end so as to span thecentral one of said rings to disrupt both the seal therewith and withthe other outer ring while maintaining the seal at said one outer ring.

3. In a control valve, the combination of a housing, a pair of axiallyaligned, rigid rings having accurately formed internal bores disposed insaid housing to define opposite ends of a high pressure chamber, a thirdrigid ring having an accurately formed internal bore supported in saidhousing in substantial axial alinement with said pair for limitedtrans-axial floating movement and located to coact with one of the firstmentioned pair of rings to define the opposite ends of a low pressurechamber, and a plunger closely fitted in said bores and slidable axiallythrough said rings.

4. A valve comprising, in combination, a casing having a cylindricalbore, a valve assembly in said bore including an elongated plunger,three rigid ring members apertured to receive said plunger with asealing fit, means interposed between said rings to retain them spacedapart axially of said plunger, said plunger, said rings and said spacingmeans being assembled for insertion in said bore as a unit, two of saidrings being dimensioned for closely fitting engagement with the walls ofthe bore, the other of said rings being dimensioned to fit loosely insaid bore whereby alinement of the assembly in the bore is facilitated,and means for retaining the assembly in said bore.

References Cited in the file of this patent UNITED STATES PATENTS1,385,019 Mathieu July 19, 1921 2,118,180 Ferguson May 24, 19382,212,343 Goehring Aug. 20, 1940 2,320,905 Bateholts June 1, 19432,485,504 Morgan Oct. 18, 1949 2,506,111 Saint May 2, 1950 2,638,045Heitshu May 12, 1953 2,799,251 Newgen July 16, 1957

1. A VALVE COMPRISING A HOUSING HAVING AN ELONGATED CYLINDRICAL BOREDIVIDED INTO TWO AXIALLY ALIGNED CHAMBERS, A TUBULAR VALVE MEMBERSLIDABLE AXIALLY THROUGH SAID BORE, SAID MEMBER HAVING SLOTS AT OPPOSITEENDS SPACED APART SUFFICIENTLY TO ENABLE THE NON-SLOTTED PORTIONS OF THEMEMBER TO CLOSE THE OUTER ENDS OF BOTH CHAMBERS BY EFFECTING A SEAL WITHTHE OUTER ENDS OF SAID CYLINDRICAL BORE WHEN THE MEMBER IS LOCATED IN ACENTRAL POSITION, STOP MEANS ON SAID VALVE MEMBER COACTING WITH STOPMEANS IN THE VALVE BORE TO DEFINE THE LIMIT POSITIONS OF THE MEMBER ATEITHER SIDE OF SAID CENTRAL POSITION, SAID MEMBER IN ONE OF ITS LIMITPOSITIONS EXPOSING THE SLOTS IN ONE OF ITS ENDS TO ONE OF SAID CHAMBERSTO OPEN THE OUTER END OF SAID CHAMBER WHILE MAINTAINING THE OUTER END OFTHE OTHER CHAMBER CLOSED, AND SAID VALVE MEMBER IN THE OTHER OF SAIDLIMIT POSITIONS EXPOSING THE SLOTS IN ITS OTHER END TO BOTH OF SAIDCHAMBERS TO OPEN THE OUTER END OF SAID OTHER CHAMBER AND TO INTERCONNECTBOTH CHAMBERS AT THEIR INNER ENDS.